A separation method using a membrane has lots of advantages over the method based on heating or phase-changing. Among the advantages is high reliability of water treatment since the water purity required can be easily and stably satisfied by adjusting the size of the pores of a membrane. Furthermore, since the separation method using a membrane does not require a heating process, a membrane can be used with microorganism which is useful for separation process but may be adversely affected by heat.
Among the membrane employing separation methods is a method using a hollow fiber membrane module which comprises a bundle of hollow fiber membranes. Conventionally, the hollow fiber membrane module has been widely used in a micro-filtration field for producing axenic water, drinking water, super pure water, and so on. Recently, however, the application of the hollow fiber membrane module is being expanded to include sewage and waste water treatment, solid-liquid separation in a septic tank, removal of suspended solid(SS) from industrial wastewater, filtration of river, filtration of industrial water, and filtration of swimming pool water.
One kind of the hollow fiber membrane modules is a submerged-type hollow fiber membrane module which is submerged into a water tank filled with fluid to be treated. Negative pressure is applied to the inside of the hollow fiber membranes, whereby only fluid passes through the wall of each membrane and solid elements such as impurities and sludge are rejected and accumulate in the tank. When used for separation, the plural submerged-type hollow fiber membrane modules are installed in a frame structure. A submerged-type hollow fiber membrane module is advantageous in that the manufacturing cost is relatively low and that the installation and maintenance cost may be reduced since a facility for circulating fluid is not required.
However, when a submerged-type hollow fiber membrane module is used to treat wastewater, the solids in the wastewater fouls the membranes causing their permeability to be declined as the water treatment is processed. Thus, while the water treatment is carried out by the hollow fiber membrane module in a water-treatment tank, a maintenance cleaning has to be performed for stably maintaining the high permeability of the membranes. A typical method for the maintenance cleaning is an aeration method. In the aeration method, air is jetted from an aeration pipe positioned under the hollow fiber membrane module during the water treatment, thereby generating rising air bubbles. Thus, foreign materials are removed from the membrane surface owing to the rising air bubbles themselves and the rising water flow caused by the rising air bubbles.
However, the filtering membrane module installed to a filtering apparatus may be shaken, distorted, or vibrated due to the rising air bubbles generated for the maintenance cleaning of the filtering membrane, and the water turbulence caused by the rising air bubbles. Furthermore, a crack may occur in respective connection parts of the filtering membrane module as the filtering membrane module is shaken, distorted or vibrated.
As a result, since the filtering membrane module is frequently damaged during the maintenance cleaning, a replacement period of the filtering membrane module becomes shortened, thereby causing a serious problem of immerse replacement cost.